| Summary | This article describes how and when CORBA Callbacks should be used and the advantages and disadvantages they offer. |
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| Article Number | 19429 |
| Environment | Orbix 6.3 All Supported Operating Systems |
| Question/Problem Description | What is a CORBA Callback? How to implement callback operations in Orbix. Implementing CORBA Callbacks. Advantages to CORBA Callbacks. |
| Clarifying Information | |
| Error Message | |
| Defect/Enhancement Number | |
| Cause | A typical CORBA exchange involves Application A (The client) invoking an operation on Application B (The server). The operation blocks until Application B returns a result, or an exception is thrown. In certain circumstances, it may be preferable for Application A to invoke an operation on Application B, but for this call not to block. Instead Application B could reestablish a connection to Application A and push back its reply. This approach is called a "CORBA Callback". In the above example, Application B takes on the role of a client, while Application A takes on that of a server. |
| Resolution |
CORBA Callback objects are implemented on a client in exactly the same was as CORBA objects are on a server. CORBA Callback objects are activated in a client-side POA (Please see the section “Activating CORBA Objects” in our CORBA Programmers Guide). The CORBA Callback object's POA’s life-span policy should be set to TRANSIENT. Thus, all object references that the POA exports are valid only as long as the POA is running. This ensures that a late server callback is not misdirected to another client after the original client shuts down. As the root POA always exports transient object references, it may be appropriate to use a client’s root POA for callback objects. Using this approach, it is important to ensure the callback code is thread-safe, otherwise, the POA should be created with "SINGLE_THREAD_MODEL" and "TRANSIENT" policies. |
| Workaround | |
| Notes | For further details on implementing CORBA Callback objects, please see the section entitled "Implementing Callback Objects" in the Orbix Programmer's Guides. |
| Attachment |
| Created date: | 06 September 2011 |
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| Last Modified: | 13 February 2013 |
| Last Published: | 23 June 2012 |
| First Published date: | 10 September 2011 |
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